Method and apparatus for optical interferometric measurements with reduced sensitivity to vibration

Claim 1

A method for providing interferometric measurements having reduced sensitivity to vibration comprising the steps of: amplitude splitting an interference pattern into a first and a second interferogram: imaging said first interferogram onto a first detector having a first data acquisition rate for acquiring a first data set of interferograms; imaging said second interferogram onto a second detector having a second data acquisition rate for acquiring a second data set of interferograms, said second data acquisition rate being different than said first data acquisition rate, with said first data acquisition rate comprising a first frame rate for providing a first data set as said first data set and said second data acquisition rate comprising a slow frame rate for providing a slow data set as said second data set; providing substantially identical frame integration periods which overlap in time said first and second detectors; analyzing said first data set for phase for said interferograms in said fast data set and analyzing said first data set for phase at each image point on each frame of said fast data set; determining a phase difference between said interferograms in said slow data set from said phases derived from said fast data set; and analyzing said slow data set with said phase differences while accounting for non-equal phase separations between interferograms; wherein the phase separation between acquired interferograms may be dynamically measured while enabling correction of phase errors due to instrument inaccuracies and external vibrations calculating a phase increment between each frame in said slow data set using said fast data set using said fast data set phases and analyzing said low data set for phase at each image point using said calculated phase increments.

Claim 2

A method for providing interferometric measurements having reduced sensitivity to vibration comprising the steps of: amplitude splitting an interference pattern into a first and a second interferogram: imaging said first interferogram onto a first detector having a first data acquisition rate for acquiring a first data set of interferograms; imaging said second interferogram onto a second detector having a second data acquisition rate for acquiring a second data set of interferograms, said second data acquisition rate being different than said first data acquisition rate, with said first data acquisition rate comprising a first frame rate for providing a first data set as said first data set and said second data acquisition rate comprising a slow frame rate for providing a slow data set as said second data set; providing substantially identical frame integration periods which overlap in time said first and second detectors; analyzing said first data set for phase for said interferograms in said fast data set and analyzing said first data set for phase at each image point on each frame of said fast data set; determining a phase difference between said interferograms in said slow data set from said phases derived from said fast data set; and analyzing said slow data set with said phase differences while accounting for non-equal phase separations between interferograms; wherein the phase separation between acquired interferograms may be dynamically measured while enabling correction of phase errors due to instrument inaccuracies and external vibrations calculating a phase increment between each frame in said slow data set using said fast data set using said fast data set phases and analyzing said low data set for phase at each image point using said calculated phase increments.

Claim 21

A system for providing interferometric measurements having reduced sensitivity to vibration comprising: a source of illumination interferometer means comprising an interferometric objective having a reference path and a test path, said illumination source producing a light beam for entering said interferometer for providing a light beam along each of said paths which combine at the output of said interferometer means to produce an interferogram; phase shifting means associated with said interferometer means for varying the length of one of said paths by a controlled amount; beam splitter means disposed with respect to said interferometer means output for amplitude splitting said recombined interferogram into first and second imaging interferograms; first and second detector means each having a different data acquisition rate, said first detector means having a fast frame rate for acquiring a fast data set of interferograms and said second detector means having a slow frame rate for acquiring a slow data set of interferograms, said beam splitter means imaging said first and second imaging interferograms onto said first and second detector means respectively, said first and second detector means comprising image fields and being disposed such that said image fields substantially overlap and are synchronized with each other so that the frame imegration periods are identical and overlap in time; said phase shifting means changing said phase difference between beams in said interferometer means during data acquisition; and means for analyzing said fast data set of interferograms for phase, determining a phase difference between said interferograms in said slow data set from said phases derived from said fast data set, and analyzing said slow data set with said phase differences while accounting for non-equal phase separations between interferograms; wherein the phase separation between acquired interferograms may be dynamically measured while enabling correction of phase errors due to instrument inaccuracies and external vibrations; means for calculating the phase at each image point on each frame of said fast data set during data analysis and calculating a phase increment for each image point of said fast data set phases.

Claim 22

A system for providing interferometric measurements having reduced sensitivity to vibration comprising: a source of illumination interferometer means comprising an interferometric objective having a reference path and a test path, said illumination source producing a light beam for entering said interferometer for providing a light beam along each of said paths which combine at the output of said interferometer means to produce an interferogram; phase shifting means associated with said interferometer means for varying the length of one of said paths by a controlled amount; beam splitter means disposed with respect to said interferometer means output for amplitude splitting said recombined interferogram into first and second imaging interferograms; first and second detector means each having a different data acquisition rate, said first detector means having a fast frame rate for acquiring a fast data set of interferograms and said second detector means having a slow frame rate for acquiring a slow data set of interferograms, said beam splitter means imaging said first and second imaging interferograms onto said first and second detector means respectively, said first and second detector means comprising image fields and being disposed such that said image fields substantially overlap and are synchronized with each other so that the frame imegration periods are identical and overlap in time; said phase shifting means changing said phase difference between beams in said interferometer means during data acquisition; and means for analyzing said fast data set of interferograms for phase, determining a phase difference between said interferograms in said slow data set from said phases derived from said fast data set, and analyzing said slow data set with said phase differences while accounting for non-equal phase separations between interferograms; wherein the phase separation between acquired interferograms may be dynamically measured while enabling correction of phase errors due to instrument inaccuracies and external vibrations; means for calculating the phase at each image point on each frame of said fast data set during data analysis and calculating a phase increment for each image point of said fast data set phases.